The present invention relates to a skin perfusion evaluation apparatus and method. More particularly, the present invention relates to an apparatus and method for rapidly assessing microvascular profusion of the skin which is capable of providing an indication of vascular sufficiency in the tested area.
The apparatus of the present invention is particularly effective in early detection of pressure ulcers to permit treatment before such pressure ulcers (i.e. bed sores) develop. When a patient is bedridden, soft tissue is often compressed for a long period of time between a bone of the patient and a firm surface such as a mattress. This can cause a localized area of tissue necrosis which is a pressure ulcer, decubitus ulcer, or bed sore. The relationship between microvascular blood flow (perfusion) in the skin and an external pressure force applied to the skin is important in the determination of the likelihood of pressure ulcers occurring in the particular tested region.
An object of the present invention is to provide a rapid and non-invasive method for evaluating microvascular perfusion of the skin.
It is known that temperature of the skin resulting from intrinsic or non-environmental factors is primarily produced by blood perfusion. The present invention provides a handheld mechanism for rapidly assessing perfusion of the skin. The apparatus forces blood from an area of the skin and monitors reperfusion in the area to determine the sufficiency of the perfusion. If blood reperfuses quickly to the area where the pressure has been applied, the patient is less likely to have a pressure ulcer formed in that area. By determining the likelihood for development of pressure ulcers before the pressure ulcers actually occur, it is possible to take preventative steps to prevent pressure ulcers. For instance, the patient could be transferred to a different bed which reduces pressure on the body. The patient can be monitored more closely to make sure that pressure on a particularly vulnerable area is avoided. Therefore, by providing rapid assessment of microvascular perfusion in a particular area, the present invention can reduce the likelihood of development of pressure ulcers, thereby reducing pain and suffering to the patient and reducing costs associated with treating pressure ulcers after they develop.
The apparatus and method of the present invention is also useful for diabetics. The apparatus and method for evaluating skin perfusion can be used to monitor and detect vascular insufficiency in the legs before the insufficiencies lead to leg ulcers and other problems. The apparatus and method of the present invention is useful in any instance where determination of reduced blood flow in an area can result in earlier treatment (i.e. tissue flaps and graphs).
According to one aspect of the present invention, an apparatus is provided for evaluating perfusion adjacent a skin surface. The apparatus includes a housing having first and second interior regions. The housing is configured to engage the skin surface. The apparatus also includes a plunger located in the first region of the housing for applying pressure to a first zone of the skin surface, and a vacuum connection coupled to the second region of the housing to permit suction to be applied to the second region of the housing and to a second zone of the skin surface. The apparatus further includes a first temperature sensor located in the first region for generating an output signal related to the temperature of the first zone of the skin surface, a second temperature sensor located in the second region for generating an output signal related to the temperature of the second zone of the skin surface, and a processor circuit coupled to the first and second temperature sensors for determining a differential temperature between the first and second zones of the skin surface to provide an indication of blood perfusion and vascular sufficiency.
In the illustrated embodiment, the first region of the housing is defined by a central bore for receiving the plunger, and the second interior region of the housing surrounds the first region and the plunger. The apparatus includes a resilient sleeve having a first end coupled to the plunger and a second end coupled to the housing to secure the plunger to the housing for reciprocating movement within the first interior region of the housing. The suction in the second region of the housing automatically forces the plunger downwardly in the first region to engage the first zone of the skin surface located below the first region of the housing.
Also in the illustrated embodiment, the first temperature sensor includes a first plate and a first bank of thermistors located adjacent the first plate for detecting temperature changes in the first plate. The first bank of thermistors is coupled to the processor circuit. The second temperature sensor includes a second plate and a second bank of thermistors located adjacent the second plate for detecting temperature changes in the second plate. The second bank of thermistors is coupled to the processor circuit.
The apparatus includes a display coupled to the processor circuit. Therefore, the processor circuit displays the indication of perfusion on the display. The apparatus may also include a heat source coupled to the processing circuit for heating the skin surface adjacent the housing to a base temperature, or a cooling source coupled to the processing circuit for cooling the skin surface adjacent the housing to a base temperature.
According to another aspect of the present invention, a method is provided for evaluating microvascular perfusion adjacent a skin surface. The method includes the steps of applying a positive force to a first zone of the skin surface, and applying a negative force to a second zone of the skin surface. The method also includes the steps of measuring a microvascular perfusion rate (i.e. rate of perfusion) in the first zone, measuring a rate of perfusion in the second zone, and calculating a differential rate of perfusion between the first and second zones of the skin surface to provide an indication of microvascular perfusion adjacent the skin surface.
Illustratively, the step of measuring the rate of perfusion in the first zone includes the step of measuring a temperature of the skin surface in the first zone, the step of measuring the rate of perfusion in the second zone includes the step of measuring a temperature of the skin surface in the second zone, and the step of calculating a differential rate of perfusion includes the step of calculating a differential temperature between the first and second zones of the skin surface. The method further includes the step of displaying the indication of perfusion.
The second zone of the skin surface may surround the first zone, or the first and second zones of the skin may be spaced apart from each other. The method may also include the step of heating the first and second zones of the skin surface to a base temperature prior to the applying steps, or the step of cooling the first and second zones of the skin to a base temperature before the applying steps.
According to yet another aspect of the present invention, an apparatus is provided for evaluating perfusion adjacent a skin surface. The apparatus includes a housing, and a plunger movably coupled to the housing. The plunger is configured to apply a predetermined pressure to the skin surface. The apparatus also includes a temperature sensor for measuring a temperature of the skin surface below the plunger, and a processor circuit for calculating a differential temperature between a first reference temperature measured by the sensor before pressure is applied to the skin surface by the plunger and a second temperature measured by the sensor after pressure is applied to the skin surface by the plunger. The differential temperature provides an indication of perfusion in the skin surface.
In the illustrated embodiment, the housing has an interior region and a portion of the plunger extends into the interior region of the housing. The apparatus also includes a spring located in the interior region of the housing for applying a biasing force to the plunger so that the plunger applies the predetermined pressure to the skin surface.
The temperature sensor may be an infrared transmitter and a thermopile coupled to the processor circuit. In this embodiment, the plunger includes a central passageway defining a wave guide. The infrared temperature sensor is mounted on an end of the plunger in communication with the wave guide. The apparatus further includes a sapphire window coupled to a second end of the plunger spaced apart from the infrared sensor.
The processor circuit provides the indication of perfusion in less than one minute, preferably in less than 30 seconds. The apparatus is a hand held unit and the processor circuit and temperature sensor are operated by a battery. The apparatus includes a display coupled to the processor circuit. The processor circuit provides a visual indication of perfusion on the display. In one embodiment, the processor circuit evaluates a magnitude of the differential temperature to provide the indication of perfusion.
According to still another aspect of the present invention, a method is provided for evaluating perfusion adjacent a skin surface. The method includes the steps of measuring a reference temperature of the skin surface, storing the reference temperature, and applying a positive force to the skin surface. The method also includes the steps of measuring a temperature of the skin surface after the positive force is applied, and calculating a differential temperature between the reference temperature and the temperature after the positive force is applied to provide an indication of perfusion adjacent the skin surface. The method further includes the step of displaying the indication of perfusion.
According to a further aspect of the present invention, a method is provided for evaluating perfusion adjacent a skin surface. The method includes the steps of measuring a reference rate of perfusion of the skin surface, storing the reference rate of perfusion, and applying a positive force to the skin surface. The method also includes the steps of measuring a second rate of perfusion adjacent the skin surface after the positive force is applied, and calculating a differential rate of perfusion between the reference rate of perfusion and the second rate of perfusion after positive force is applied to provide an indication of perfusion adjacent the skin surface. The method further includes the step of displaying the indication of perfusion.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.